2 THE CHEMICAL CONSTITUTION OF THE PROTEINS 



(V) Giucoproteins -. Carbohydrate in combination with protein, 



e.g., mucin, ovomucoid. 

 X. Derivatives of Proteins : 



(a) Metaproteins, e.g., acid-albumin, alkali-globulin. 



(b) Proteoses, e.g. t caseose, albumose, globulose. 



(c) Peptones, e.g., fibrinpeptone. 



(cT) Polypeptides, e.g., glycyl-alanine, leucyl-glutamic acid, 



a tetrapeptide (2 glycine + I alanine + i tyrosine). 

 Except the protamines, the histones, and the derivatives of the 

 proteins, all the proteins contain carbon, hydrogen, nitrogen, sulphur 

 and oxygen, and they possess the following elementary composition : 



C 51-55 per cent. 

 . H ' 7 

 N 15-19 

 S 0-4-2 '5 

 O 20-30 



from which a formula such as 



^726 " 1174 194^3O214> 



which is that of globin, the basis of haemoglobin, can be calculated. 



The phosphoproteins and the nucleoproteins contain also the 

 element phosphorus ; in the former, probably combined directly with 

 one of the constituents of the protein molecule ; in the latter, combined 

 with a pyrimidine or purine base or a carbohydrate ; these substances, 

 together with phosphorus, constitute nucleic acid. 



Investigations upon their chemical constitution have been carried on 

 now for nearly a century, but it is only since 1901 that, by the work 

 of Emil Fischer and his pupils, any clear view has really been obtained 

 of their actual constitution. The main result of these investigations 

 is that the protein molecule is built up of a number of amino acids, 

 belonging to four different series, and of which the following have 

 been definitely determined : 



A. Monoaminomonocarboxylic acids. 



1. Glycine, C 2 H 5 NOr>, or amino-acetic acid. 



CH 2 . (NH 2 ) . COOH 



2. Alanine, C 3 H 7 NO. 2 , or o-aminopropionic acid. 



CH, . CH(NH 2 ) . COOH 



3. Valine, C 5 H n NO 2 , or o-aminoisovalerianic acid. 



CH 3 \ 



)CH . CH(NH 2 ) . COOH 

 CH 3 X 



